Information about the novel coronavirus (the virus that causes COVID-19) is constantly evolving. We will refresh our novel coronavirus content periodically based on newly published peer-reviewed findings to which we have access. For the most reliable and up-to-date information, please visit the CDC website or the WHO’s advice for the public.
TABLE OF CONTENTS
- Types of COVID-19 tests
- What do sensitivity and specificity mean in COVID tests?
- What are PCR tests?
- How do PCR tests work?
- What are antigen / rapid antigen tests?
- How do antigen tests work?
- What are antibody tests?
- When should I get a test?
- Which test is right for me?
- How long does a test take?
- Where and for how much can I get a test?
- Which tests can be done at home?
- What should I do if I test positive?
- If I test negative, can I go visit my family?
Whether you’re a coronavirus expert or are just learning about it now, there’s an overwhelming amount of COVID-19 information out there (some accurate, some not so much).
Don’t worry—we’ve broken down the science, and pulled together everything you need to know about COVID testing. Read on to find out more about how well each test works, and what you should do if you test positive.
- There are three main types of COVID tests: PCR tests that look for the virus’s genetic material, antigen tests that look for the virus’s outer shell, and antibody tests that look for your body’s response to the virus. Scientists measure how accurate a test is based on how often it correctly identifies people infected with the virus and how often it correctly identifies people who are not. PCR and antigen tests determine if you have the virus in your body at the time you are tested. PCR tests are very good at catching almost all cases of COVID, but they can be expensive and take longer to process. Antigen tests might not catch as many cases, but they’re faster, less expensive, and don’t require any special machinery. Antibody tests look at your body’s reaction to the virus, and can be used to see if you have had the virus in the past or have been vaccinated against it.
What are the different COVID tests and how do they differ?
There are three different types of COVID tests commonly used (La Marca, 2020):
- PCR tests: These tests look for the virus’s genetic material.
- Antigen tests: These look for the presence of viral proteins, like the spiky outer shell of the coronavirus.
- Antibody tests: These tests look for your body’s reaction to the virus, and are an indication that you’ve already had COVID.
When it comes to deciding which test is the best option for you, there are a few things to consider. Do you want to know whether you have the virus now, or if you’ve had it in the past? What test you take also depends on how soon you need the results. Price and availability are both critical factors, too.
Before we explain each test in more detail, let’s look at the two main factors scientists and health professionals use to assess the accuracy of COVID tests: sensitivity and specificity. If these sound complicated, don’t worry—they’re not. They can be a little confusing, though (even for medical professionals), so we’ve explained it here.
What do sensitivity and specificity mean when it comes to COVID tests?
Sensitivity and specificity are terms used to describe how accurately a test does the job it was designed to do (Swift, 2020). To understand how it works, here’s an example.
Imagine we have two people. One person, we’ll call him Dan, has COVID. The other person, we’ll call him Stan, does not.
Dan has COVID, takes a test, and the test is positive (confirming that Dan has COVID). We call that a true positive because it’s true that he’s positive for the virus. But what happens if, by mistake, that test says Dan doesn’t have COVID, even though he does? We call that a false negative because it’s false that he’s negative.
Still with us? Okay.
This is Stan, who doesn’t have COVID. He takes a test and it comes back negative, confirming he doesn’t have it. We call that a true negative because it’s true that he’s negative. If the test incorrectly says Stan has COVID, that would be a false positive because (you guessed it) it’s false to say he’s positive.
To sum up, the sensitivity of a test is how good it is at finding people who have COVID (the rate of true positives). If a test is 98% sensitive, for example, it means that out of 100 people who have COVID, the test is positive in 98 cases. Basically, it has a high rate of true positives and a low rate of false negatives.
While sensitivity focuses on people who have COVID, specificity focuses on those who don’t. A test that’s 98% specific means that out of 100 people who don’t have COVID, it will correctly identify 98 who are COVID-free. But it’s also saying that two people are positive for COVID, even though they don’t actually have it—a high rate of true negatives and a low rate of false positives.
So how does this work in the real world? Let’s try our little experiment again. Imagine this time you have 200 people. One hundred of them have COVID, and 100 don’t. If your test is 100% sensitive and 100% specific, the results will show exactly that—100 people have COVID and 100 don’t.
When it comes to developing tests, we want ones that identify all the people who have COVID as being positive: high sensitivity. We also want to make sure the test doesn’t accidentally say a person has COVID when they don’t.
A good example of this is an airport security checkpoint. Their test is a metal detector, which detects any weapons that contain metal. That means the test has high sensitivity for metal weapons. However, detectors also beep if encountering a belt, watch, aluminum water bottle, and anything else made of metal (so they’ve got lots of false positives). That’s because these detectors have low specificity, or are not specific to weapons.
In the case of airport security, this might just be a time-consuming inconvenience. But when it comes to medical tests, we often need to be more careful. Here’s why.
It’s clear why having a test with high sensitivity is important: we want to catch every case of COVID to prevent the further spread of the virus. But who cares if a test isn’t specific? What difference does it make if a few healthy people are misdiagnosed with COVID?
A positive COVID test can significantly disrupt a person’s life. They might have to miss work or pull their kids out of school. It can be stressful and complicated to identify all of the people you may have been in contact with to warn them as well.
That’s why scientists strive for the highest rate of sensitivity and specificity possible. But there are trade-offs. Let’s take a closer look at each test, how it’s performed, and how they all compare.
What is a PCR test?
PCRs are laboratory tests used to identify genetic material. PCR tests use special particles that light up when exposed to the virus’s genetic material, which can be found inside the virus’s outer capsule and is also known as viral RNA.
One of the most amazing things about PCR tests is that they multiply the sample. That means even if there’s a tiny bit of the virus’s genetic material in your sample, the test will find it, making it super sensitive (Yohe, n.d.).
Genetic material is very fragile and disappears quickly, so a positive PCR test is a pretty good indicator that a person currently has the virus in their system. But just because you have the virus’s genetic material in your body, doesn’t always mean you’re contagious. And while this can be a good thing, it can also be a problem. Scientists estimate those with COVID can infect other people for up to three days before any symptoms show up. People infected with the virus are also most likely to infect others around the time their first symptoms appear (He, 2020).
Even after you’re no longer infectious, the PCR test can remain positive for as long as 90 days. It’s a good way to make sure you catch nearly every case, but not a great way to determine if you’re still at risk of infecting others. That’s why if you’ve already tested positive, you can’t use a PCR test to decide when to stop quarantining (CDC, 2021a).
How does a PCR test work?
Think of genetic material like a long chain of those letter beads you used to make necklaces out of at summer camp. Each sequence of beads is unique to a particular animal, plant, or virus. PCR tests work by making little copies of the genetic material. That means even if only a tiny bit of the virus was present in your sample, scientists will still be able to find it.
Once lots of copies are made, the test uses small particles that light up when they come into contact with genetic material from the virus. But what if the sample doesn’t contain a viral sequence? In that case, nothing lights up and the test is considered negative.
To perform a PCR test, a nasal swab is placed up your nose to get a sample. Alternatively, you can spit saliva into a tube. And while your sample can be collected anywhere (at home, in a lab, or at a pharmacy), the sample has to be processed by a special machine in a lab. This can take hours or even days to get results, depending on the facility.
Fortunately, you can be pretty confident that your test is accurate because PCR testing is highly sensitive. Like any test, however, there’s room for user error. While tests are about 100% sensitive in the lab, in real life, it may be more like 80%. That means that for every 100 people with COVID, this test identifies about 80 of them (Yohe, n.d.).
Since it’s possible to miss a person who has COVID when using this test, most healthcare providers will look for other clues, like symptoms and potential exposures, when interpreting a negative PCR result. No test is 100% accurate all of the time, but PCR tests are currently the recommended test for diagnosing COVID (La Marca, 2020).
What are antigen tests?
Antigen tests look for what’s called the capsid, or the outer shell of the virus. Each virus has unique features. In the case of the coronavirus, you may recognize the characteristic “spike proteins” on its outer shell. These spikes form a sort of crown around the virus, giving it its name (“corona” means crown in Latin) (Chorba, 2020).
Antigen tests look for these spike proteins—kind of like checking IDs at the entrance to a club—to tell if the virus is in your body (Chorba, 2020). The best part about these tests is they can be performed quickly, and in some cases, can even be done in the comfort of your own home. Unlike PCR tests, antigen tests don’t need a big expensive machine to be evaluated (FDA, 2020).
In fact, some of these tests are available as at-home kits that take just 15 minutes from start to finish. If this seems a little too good to be true, there is a catch. Tests need to be done properly, and doing one at home means there likely isn’t an experienced medical professional around to make sure you’re doing it correctly. If the sample isn’t collected properly, your test might be negative even though you have the virus (Yohe, n.d.).
Another concern is antigen testing isn’t quite as sensitive as other tests that look for genetic material, so they might miss some cases of COVID. But researchers point out that antigen tests are more sensitive when a person is still infectious, so the ease and speed with which these tests can be performed means they could curb outbreaks better than more sensitive tests, like PCRs (Mina, 2020).
What is a lateral flow antigen test and how does it work?
A lateral flow antigen test is just a fancy term for a simple, easy-to-use test that detects a certain molecule in a sample. A great example of this type of test is a pregnancy test. When a person is pregnant, their body contains higher levels of the hormone HCG, which is present in their urine. Pregnancy tests involve peeing on a stick, and if HCG is present, a line appears on the test indicating that they’re pregnant (Koczula, 2020).
The same principle applies to the COVID test, except here, we’re looking for protein from the virus’s outer shell, and samples are collected from the mouth or nose rather than from urine (Chen, 2005).
The test works through what’s called the sandwich method. Researchers developed a small test strip that contains magnet-like particles that only stick to COVID proteins. If those proteins are present, another indicator substance can bind, too. If it binds, the test strip will reveal a colored line on it. If there’s no COVID in the sample, the indicator can stick, leaving no color on the strip (Chen, 2005).
What are antibody tests?
Antibody tests (not to be confused with antigen tests) look for your body’s response to the virus. While that’s not where the name comes from, it’s a nifty way to remember what it means. Every time we get exposed to an invading pathogen, like a virus or bacterium, our immune system generates antibodies that help us fight it.
In other words, antibody tests can tell if your immune system has been exposed to the virus (through infection) or to a piece of the virus (through vaccination). Healthcare providers may recommend getting this test if you think you’ve had COVID in the past, but never got tested. While this may mean that it’s less likely you’ll catch COVID again, researchers aren’t sure how long this protection will last. For some viruses (like the virus that causes Chicken Pox) the protection can be life-long for some people. For other viruses (like the flu), antibodies might only protect you for a few months to a year.
When it comes to the COVID antibody test, sample collection (typically a blood draw) can be done at a pharmacy, testing center, hospital, and in some cases, at home. Serology tests are typically evaluated in a laboratory but at-home tests may be more readily available in the future.
When should I get a test?
According to the Centers for Disease Control and Prevention (CDC), you should get tested if you’ve been exposed to a person who has tested positive for the coronavirus or if you have symptoms of COVID-19.
In an ideal world where COVID tests are readily available, inexpensive, or even free, more testing is always better. Unfortunately, we’re not quite there yet, so the CDC has worked hard to establish clear guidelines to help you decide whether or not to get tested. If you fall into any of the categories below, the CDC recommends getting tested (CDC, 2021b):
- If you have symptoms of COVID
- If you’ve been in close contact with (at least 15 minutes within six feet of) a person who has tested positive for COVID
- If you’ve are unvaccinated and have been in a situation where it wasn’t possible to socially distance, like travelling through an airport or attending a large gathering
- If you’ve been asked to be tested by a healthcare provider or your local health department
While you’re waiting for your test results, it’s important to quarantine—including from the members of your own household, if possible.
Which test is right for me?
Choosing a test depends on your circumstances, and in some cases, you might not get to pick.
When it comes to determining whether you have a COVID infection right now, your options are PCR and antigen testing. If you can get access to a test through your workplace, insurance, healthcare provider, or local health department, they will likely choose based on price and availability (CDC, 2020).
For many people, particularly those who had symptoms of COVID early in the pandemic, an antibody test might be able to confirm if they’ve had COVID. A positive antibody test can also show that you have been vaccinated against coronavirus. That being said, antibodies don’t necessarily stick around forever. There have been instances of people who had COVID antibodies after being sick, but no longer had them when getting tested again a few months later.
How long does a test take?
Collecting the actual sample is usually pretty quick. Depending on the type of test, you may have your nose (or less commonly your mouth) swabbed with a cotton swab. While nasal swabs can be a little uncomfortable, it’s crucial that it’s done right to ensure optimal accuracy. In other cases, you may be asked to spit into a small test tube.
How long it actually takes to get the results of a COVID test depends on a few factors. Rapid antigen testing takes around 15 minutes from sample collection to results, but there may be things that delay your results. For example, tests might be collected at one site, and then processed at another. Recently, the U.S. Food and Drug Administration (FDA) granted emergency use authorization for certain at-home COVID tests, some of which send results directly to your smartphone in just 15 minutes (FDA, 2020).
As we mentioned earlier, PCR test samples have to be processed using a special machine. These PCR machines are typically available in labs and hospitals, not clinics or pharmacies. Some pharmacies and testing centers offer results within 24 hours, but people have reported waiting nine days or longer before getting results (NPR, 2020).
Where can I get a COVID test, and how much will it cost?
The cost of COVID tests varies from provider to provider, and from location to location. The U.S. Department of Health and Human Services has a tool you can use to identify testing options in your state (HHS, 2020).
Federal law established at the start of the pandemic set aside resources for granting access to testing for people without insurance. It required that COVID testing and associated treatment be covered for people with private insurance, Medicare, or Medicaid. That said, there was no rule guaranteeing free testing. Based on the Peterson Center on Healthcare and the Kaiser Family Foundation Health System Tracker, which evaluates the average cost of different COVID tests, test prices for PCR tests ranged from $20–$850.
If you think you need a COVID test, your best bet is to contact a healthcare provider. They may be able to give you guidance as to whether or not you should come in for testing, and what your best options are for getting a test.
You can also check your local health department’s website to get information about testing options and sites. If you’re feeling cold-like symptoms and suspect you might have COVID, it’s best to start by isolating yourself from others. You may be advised not to come in for testing, and simply quarantine yourself at home so as not to expose anyone outside the house.
Which tests can be done at home?
As the pandemic wears on, more test options are becoming available, including rapid antigen tests that can be performed at home. So far, the FDA has authorized a number of tests that can be collected at home. Some require a prescription while others do not, and some can be evaluated using your smartphone while others need to be sent into a lab to be processed. Some are covered by insurance, and others require out of pocket payment. The list of currently available at-home COVID tests is available from the FDA (FDA, 2020).
What should I do if I test positive?
If you test positive for the coronavirus, the CDC recommends that you isolate at home, including away from people who live there, too. It’s okay to stop isolating once the following conditions have been met (CDC, 2021d):
- At least 10 days have passed since a positive test and you didn’t have any symptoms
- At least 10 days have passed since symptoms first appeared
- You have been fever-free for at least 24 hours without using fever-reducing medication, and any other COVID symptoms are improving
It’s important to know that loss of taste and smell may persist for weeks or even months after recovering, and are not a sign of being infectious.
How long was I infectious before I had symptoms?
Researchers have found that people can spread the coronavirus before they even feel sick. On average, they determined that you’re likely to spread the virus as early as 2–3 days before your first symptoms appear (He, 2020).
Some people never develop symptoms. If you test positive or were exposed to someone who tested positive for COVID, quarantine at home for 14 days before leaving isolation (CDC, 2021e).
I tested positive. Who should I tell?
Since you can spread the virus before feeling sick, try to trace your steps and identify all the people you came in contact with during the days prior to your first symptoms (He, 2020). This may include your workplace, friends or family you visited, anyone who came to your home, and more. You should also assume that other members of your household have been infected as well. That means notifying their contacts, workplaces, or schools.
If you live with others (especially if you share a bathroom or spend time together without masks on), it’s possible that they’re already infected. Still, it’s important to isolate from them if possible to ensure that they don’t become infected if they haven’t already.
There’s no doubt it can be stressful letting people know you’ve tested positive. You may be concerned that people will judge you, or be angry with you. But keep in mind, even people who’ve followed the strictest protocols for preventing COVID have been infected. And of course, one of those close contacts you need to alert might be the person who infected you in the first place.
Most cases of COVID are mild and do not require medical attention, but it’s important to stay at home for 14 days after your first positive test result to limit the virus from spreading further (CDC, 2021e).
When should I seek medical attention?
The most common symptoms of COVID—cough, fatigue, muscle aches, fever, and chills—can likely be handled from the comfort of your own home. If you feel sick, but not too sick, stay home and avoid coming into contact with others.
However, if you start to develop emergency warning signs for COVID, then you should seek medical attention immediately. These emergency warning signs include (CDC, 2021f):
- Increased difficulty breathing
- Chest pain or pressure
- New confusion
- Can’t wake up or stay awake
- Bluish lips or face
If you cannot get to a healthcare provider quickly, call 911 or call ahead to your local emergency facility to let them know about these symptoms, and that you’re concerned about COVID.
If I test negative, can I visit my family?
Unfortunately, COVID tests are just a momentary snapshot of your status. This means that even if they were 100% accurate, a negative test only means you didn’t have COVID at the precise moment it was collected. Even a few minutes after you took your test, any trip to the grocery store, hair salon, or playground could result in an infection. If you are vaccinated you are less likely to get sick, but you can still transmit the virus to others if you get infected.
That being said, being vaccinated against COVID and getting tested when needed are excellent ways to reduce the transmission of the virus. But until the pandemic is entirely under control and we have a much larger testing capacity, it’s a good idea to keep up the hard task of socially distancing when indoors, wearing masks when indicated, and avoiding large crowds of people outside of your household (especially if you are not vaccinated) (CDC, 2021g).
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